1. Field of the Invention
The present invention relates to mobile communications devices such as pagers and cellular telephones and to methods for increasing battery life, on any single charge, by reducing power draw by putting the device into standby operation sooner than IS-136 procedures otherwise call for.
2. Related Art
One of the main objectives of Industry Standard 136 of the Telecommunications Industry Association ("TIA") and the Electronic Industies Association ("EIA") is to improve battery savings in time division multiple access ("TDMA") mode digital mobile communications equipment, called "mobile stations". Battery savings is accomplished by reducing the time that the mobile station must read data among slots that are broadcast by a base station. Ideally, the mobile station needs to read, at full internal processing power, only one TDMA block of every 64 transmitted, thus for 0.02 second of each 1.28 second block, until it determines that a message is coming to it. See FIG. 2A. The device can "sleep" in a standby mode, at a low power state, for the remaining 1.26 seconds, or over 98.4% of the time, if no message is coming, yet be immediately ready to receive messages transmitted. If a paging frame class of greater than I is used by the base station, yet greater battery life is possible.
When more than five mobile stations require access simultaneously to messages from the base station, each mobile station must generally read more data of each TDMA block, draining its battery more quickly, if messages are not to be delayed in reaching the mobile station. Up to five mobile stations may use each TDMA block simultaneously without increasing battery drain in the mobile stations or delaying the sending of messages.
Paging Channel ("PCH") Displacement allows the base station to require each mobile station to read extra "SPACH" slots (SPACH is short for combined "Short message service", "Paging channel", and "Access response CHannel" communications modes or types), or "frames", in the broadcast transmission in order to determine what portions of a broadcast to greater than five mobile stations are being directed to the particular station. The base station's Page Continuation ("PCON") bit, in the Paging Channel slot, is received and read at full internal power by the mobile station once in every 64 TDMA blocks. If so directed by the PCON bit in the PCH Displacement signal, the mobile station then will also read additional SPACH slots, also at full internal power. See FIGS. 2B and 2C.
"Paging Channel Continuation" protocol is used to determine which SPACH slots or frames the mobile station should read in a broadcast transmission, i.e, those slots or frames that may be directed to it rather than to other mobile stations. The PCH continuation information is, by IS-136 standards, included in the first SPACH slot or frame in the series, if any (there usually are), in a message transmission, to direct the mobile station to the specific slots that it is to read. See FIG. 2C
For example, as explained in section 4.8 of IS-136.1 Rev A (July 1966), a full-rate digital communications channel for a mobile station may have a PCH subchannel corresponding to a super frame phase ("SFP") of 27. Even if the mobile station determines there is no message directed to it, and if page continuation is set to 1 and the paging channel displacement to 4, it will nonetheless read SFP slots 29 and 31 (=27+4) in the primary superframe and also will read slots "n+1" and "n+3" in the next primary superframe, but receive no message for itself. See FIGS. 2B and 2C. Then the mobile station enters its low power state until the next occurrence of its assigned PCH subchannel. Reading these additional four slots reduces power savings from 98.4% (63/64ths) to 92.2% (59/64ths), or increases power consumption by about 400% over the resting state.